1. Technical Field
The invention relates to power take off systems for utility vehicles and more particularly to a system providing remote starting and stopping of the vehicle and for control of an emergency back up motor to the power take off system.
2. Description of the Problem
Utility vehicles are often advantageously supplied with auxiliary equipment the operation of which is supported by the vehicle. Such auxiliary equipment can include hydraulically powered, aerial lift buckets that are often used for the repair of electrical power distribution lines. Typically, a hydraulic lift platform will be driven by a pump which is in turn driven by the vehicle""s engine. In some applications, a back up prime mover, e.g. an electrical motor, is provided for the pump. A bucket at the end of the aerial lift system is electrically isolated to allow the worker to work on power lines which are still hot.
Trucks may come equipped with controls to allow a worker supported in the bucket to remotely shut off and turn on the vehicle""s engine and to remotely raise and lower the lift. To avoid providing a conductive electrical path between the bucket and the truck, the controls located in and around the bucket for the operator""s use are usually pneumatic. An air line is connected between the bucket, where a plunger-actuated piston is positioned, and a pneumatic, pressure actuated, electrical switch on the truck. To avoid expense a minimal number of pneumatic lines is provided. A problem addressed by the invention is providing a single, pneumatic, pressure actuated electrical switch which can be used to both start and stop a truck""s engine, and in some applications, allow activation of a back up hydraulic pump in case of engine failure. Complicating the effort to construct such a device is the susceptibility of vehicle electronics to resetting during engine starting due to voltage fluctuations.
Industry standards specify that the bucket control for an aerial lift truck having an emergency or back up pump shall: (1) if the engine is running and the remote switch is closed (regardless of the duration for which it is held closed), shut down the engine; (2) if the remote switch is kept depressed for more than 3 seconds following a remote engine stop, cause the emergency or back up pump to operate and to continue to operate for as long as the switch is held closed; (3) if the remote switch is cycled following a remote stop or following the operation of the emergency pump, cause the engine to crank for the duration of the switch closure; and (4) if the engine does not start after cranking, respond to cycling the remote switch by causing the emergency pump to operate for as long as the remote switch is depressed.
Contemporary vehicles are commonly equipped with an electrical systems controller/body computer (ESC) and a controller area network allowing data transfer between the ESC and other controllers, including an engine controller and a transmission controller. These systems are built in conformance with the Society of Automotive Engineers"" J1939 standard. Remote engine and bucket position control must be implemented in a way that cranking and shut down of the engine is effected only by closure of a hard-wired, ground side switch. This remote switch must be designed in the system hardware and be independent of the ESC""s software. The hardware architecture cannot depend upon the ESC remaining active during engine cranking and must continue to function even if the ESC temporarily fails and reinitializes due to transient low voltage.
The status of the ESC cannot be allowed to interfere with normal starting and stopping of the engine using the standard four-position key ignition switch. It must remain possible to crank the engine even when the vehicle is latched in the remote start mode. This allows ground personnel to start the engine and engage PTO operation to lower a boom should the operator be disabled. It is permissible to allow momentary cycling of the key ignition switch to cancel remote stop mode. The system shall prevent engine cranking in response to closure of the remote switch if the hood is open. The hood disable feature must also be independently operable without reference to ESC status. However, the backup pump motor must be operable with the hood open.
The backup motor and solenoid should not be operated for any duration of time, or briefly cycled on and off, unless the conditions for emergency operation have been met. The backup motor brushes and solenoid contact life may be compromised by repeated, brief duration operation at high surge current levels. Remote switch operation should not result in application of any current to the backup motor and solenoid unless and until its operation is necessary.
The system shall permit the engine to crank only so long as the remote switch is closed. Once the remote switch opens, cranking should immediately stop, allowing only for some delay where the remote switch is pneumatically actuated. The system shall not allow the engine to crank unless the parking brake is set. This requirement can be met by modification of ESC software. The system shall not allow remote engine shut down unless a J1939 compliant engine RPM message is present on the vehicle databus from an engine controller. This requirement prevents stranding an operator in a boom since the engine will not crank remotely if an engine RPM message is not present.
According to the invention there is provided a motor vehicle having a remote switch by which the vehicle""s engine may be shut down and restarted. In some applications the same switch may be used to engage a backup electric motor energized from the vehicle""s battery as a substitute prime mover for a power take off apparatus installed on the vehicle. The invention provides a vehicle engine ignition control system having a starter solenoid and motor and engine control electronics. A multiple position ignition switch provides energization to the ignition control system in response to positioning of a key switch, as is conventional. The ignition switch has two output terminals which assume energized states in response to the positioning of the key switch. A first output is energized when the key switch in placed in a start position. A second output is energized when the key switch is in either the ignition position or the start position and may be energized when the key switch is in an accessory position. A remote switch is located on the vehicle away from the multiple position ignition switch, typically in a bucket suspended by an aerial boom. The remote switch provides a connection to ground when closed. An electrical systems controller communicates with the engine control electronics and is coupled to the remote switch to be responsive to closure of the remote switch in accordance with its programming. Responses include providing various enable signals and/or ground connections enabling operation of selected portions of the ignition control system. A remote start relay is coupled to respond to a remote start energization signal sourced by the electrical systems controller if it occurs concurrently with closure of the remote start switch. The remote start relay provides an activation signal on an output which is applied to a starter relay. The starter relay responds to the activation signal by providing activation energization to the starter solenoid and motor.
Remote stop of the engine is provided by control of a chassis ignition relay, which couples an ignition signal (Ign) from the ignition switch to an engine controller. A remote switch state detection relay is coupled to the remote switch and to-the second output of the multiposition ignition switch and is responsive to the concurrent occurrence of an energization signal on the second output of the multiposition ignition switch and closure of the remote switch to generate a remote stop energization signal. The electrical systems controller is further responsive to closure of the remote switch and to indication that the engine is operating (by reading an engine RPM signal from the engine controller) for providing a ground connection through an input. A remote stop relay provides coupling of energization from the multiple position ignition switch to the chassis ignition relay. The chassis ignition relay is connected to the remote switch state detection relay to receive the remote stop relay energization signal and is further connected to the input of the controller, the remote stop relay being responsive to the remote stop energization signal and grounding of the ground side of its energization coil through the controller input for interrupting energization of the chassis ignition relay and thereby cutting the Ign signal to the engine controller, resulting in interruption of operation of the engine.
Where a vehicle is equipped with backup prime mover for a vehicle power take off (PTO) apparatus, the ignition system further includes a backup motor and solenoid connected to the vehicle electrical power source. A backup motor inhibit relay is connected across the power connection to the backup motor and solenoid to prevent any undesired operation of the motor, however brief. A backup motor relay is coupled to receive energization from the remote start relay and is further coupled to the remote switch to be responsive to concurrent closure of the remote switch and application of the energization signal from the remote start relay for coupling energization signal from the remote start relay to the backup motor inhibit relay as an input. Finally the electrical systems controller provides a connection to ground on an inhibit input in response to the key switch being in the ignition position and engine cranking having been attempted and failed.
Additional effects, features and advantages will be apparent in the written description that follows.